Method of making calcium cyanamide



June 19, 1,928.

G. E. cox

METHOD oF MAKING cALcIUM CYANAMIJJE Filed June 17, 1925 G50/Q65 E. Co x INI/EN TOR. BYM

A TTORNEY.

Patented June 19, 1928.

UNITED STATES PATENT OFFICE.

GEORGE E. COX, OF NIAGARA FALLS, NEW YORK, ASSIGNOR TO AMERICAN CYANAMID 4COMPANY, OF NEW YORK, N. Y., A CORPORATION 0F MAINE.

METHOD 0F MAKING CALCIUM CYAN-AMIDE.

Application led .Tune 17, 1925. Serial No. 37,696.

This invention relates to an improvement in the manufacture of calcium cyanamide or lime nitrogen by the reaction between calcium carbide and nitrogen.

As described in my Patent #1,292,715, of Jan. 28th, 1919, for process and apparatus for making calcium cyanamide, calcium carbide is placed in a foraminous, cylindrical container, which is supported withina cylindrical oven, open at the top. To prevent loss of heat and to increase the efliciency of the fixation of nitrogen, a thick slab of an insulating material, such as kieelguhr, is placed on the top of the mass of carbide and an insulating cover, usually including a sand seal to prevent loss of nitrogen gas is placed thereover. The massv of carbide is locally heated electrically and nitrogen is passed in to combine with the hot carbide. The heat of the reaction is suflicient to sustain the conversion of the carbide to cyanamide and the electrical heat is cut off after the reaction is under Way.

By the use of a slab of kieselguhr I was enabled to increase the amount of nitrogen fixed', reduce the amount of unconverted carbide in the product and decrease the amount of dust resulting from imperfect fixation. However, the use of a slab of insulating material has several disadvantages. Itv cannot be made to fit perfectly along the walls of the oven and around the central electrode, because of the necessity for allowing space foi fitting the relatively large slab in place. The spaces left unprotected radiated heat v and the conversion of carbide to cyanamide vat those points was relatively low. The. slab Was thick, heavy and dense, and because of the density thereof the heat insulating effect was not perfectly satisfactory. Due to the weight and thickness of the slab it required two men with the aid of a crane to place it in its proper position, which was a tedius task, and very often the slab would crack and break during the handling since the strength vof thematerial is not very high. Even if the slab did not break it would gradually crumble away until, in a comparatively short time, it required replacement. As a result the expense of keeping the insulating slabs in proper condition was rather high.

The present invention is intended to obviate the difficulties `involved in the use of an insulating slab, it being among the objects of my invention to provide a method of covering the surface of a mass of carbide which shall be effective to protect the same and to increase the amount of conversionthereof into cyanamide by the action of nitrogen.

It is a further object of my invention to provide a method which shall be simple, shall not require the services of two men to operate and which shall obviate the necessity of forming slabs of insulating material.

In practicing my invention I provide an insulating material, such as kieselguhr, which has a high heat insulating capacity, but instead of utilizing a slab thereof I apply it in the form of a powder. The powder is light and fluffy and can be handled by one man who, after the carbide has been placed in the oven, smooths the surface thereof and then spreads out over said surface a layer of powdered kieselguhr. The fixation of nitrogen then proceeds as heretofore but the efficiency thereof is increased.

The amount of kieselguhr used is less than the amount. used in the form of a slab and the insulating effect thereof is greater than when the slab is used, because of the lower density thereof. The powder is easily applied, the operator merely spreads a bucketful of the material on the carbide and levels it off'. After thecompletion of the nitrogen fixation, the calcium cyanamide formed is in the form of a solid block or pig with the layer of powdered kieselguhr on the top. It is merely necessary to sweep the kieselguhr from the top of the pig, and it may be used over again immediately. The cost of forming the slabs for replacement` :is entirely elimina-ted and a much smaller amount of kieselguhr is used.

In the accompanying drawing constituting a part hereof, the single figure is a vertical cross-sectional view of an oven for making calcium cyanamide and embodying my invention.

The cyanamide oven used may be of any well recognized type, but I prefer to use the type of oven described and claimed in my copending application, Serial No, 37,695', filed June 17th, 1925, for eyanamide oven and assigned to the American Cyanamid Company.

The oven consists essentially of a base 1 having side walls 2 permanently secured thereto and a plurality of inlets 3 for nitrogen gas therein. Fitted on top of side walls 2 and making a gas tight seal 4 therewith is the upper portion 5 of the oven. A lining 6 of paper or similar combustible material is fitted within the walls and base of the oven and a tube 7 of similar material, in which is carried an electrode 8 of graphite, carbon or the like is inserted centrally in the oven, the lower end of the tube and of the electrode being placed in opening 9 in the refractory lining of the oven, the electrode 8 making contact with vthe steel shell of the base 1. Finely divided calcium carbide 10 is filled into the oven, the paper lining 6 preventing contact thereof with the walls of the oven and the paper tube 7 preventing contact thereof with the electrode 8. After the calcium carbide has .been filled in and the surface thereof leveled off, a layerl of powdered heat insulating material 11, such as kieselguhr powder, is spread over the surface of the carbide by hand or by means of a suitable tool such as a trowel. This can beconveniently done by taking a bucket filled with the powdered insulating material, spreading the same over the surface of the carbide by simply overturning the bucket and then smoothing out the surface thereof. The cover V,12 of the oven is then placed over the top thereof, making a gas tight seal 13 therewith. The electrode holder 14, secured in cover 12, makes good contact with the upper end of the electrode 8 and a terminal 15 is electrically connected thereto. l

Low voltage direct current is caused to flow through the electrode 8 by means of leads 16 and 17 and intermediate connections. Nitrogen gas flows through inlets 3 and is distributed substantially uniformly throughout the mass of carbide by the openings and crevices inthe base of the oven.A The heating of the electrode 8 by the current heats the mass of carbide locally, inducing a reaction `between the carbide and the nitrogen gas to form calcium cyanamide. This reaction is exothermic and r`produces sufficient heat to cause the reaction to proceed until the entire mass of 'carbide is converted into cyanamide. At the end of the reaction the product is in the -form of a block or-pig having considerable strength. In order to remove the same from the oven, the cover l2 and upper portion 5 of the oven are lifted ofi and the kieselguhr powder 11 swept from the upper surface of the pig, which may then be lifted from the lower portion of the oven by a suitable lifting device.. If desired, insteadl of sweeping oft' the kieselguhr powder from the pig, the pig may be lifted and overturned, causing the powder to fall to the ground. In either case, the powder is immediately ready for reuse without any treatment.

As the result of my invention I have xconsiderably simplified the procedure 'previ-- ously followed and have obtained increased efficiency thereby. Placiu the heat insulating material on the carbi `e is no longer an operation requiring the services of two men, often with the assistance of a crane, but a workman may throw a bucketful of the light kieselguhr powder on top of thecarbide and quickly spread the same with his hand or with a trowel uniformly over the surface of the mass. Not only is the amount of powder used far less than hitherto be- -cause it is lighter and has better insulating qualities, but also better protection is afforded thereby. The slab of kieselguhr previously used could not cover all the crevices, irregularities or corners of the oven allowing heat and gases to escape therefrom, whereas the powder, as is readily apparent, makes a perfect seal. Furthermore, I avoid the expense of molding the slabs, and at the same time obtain a higher degree of fixation of nitrogen.

Although I have described my invention setting forth a single embodiment thereof, my invention is not limited thereto as var'- ous changesmay be made within the scope thereof. For instance, instead of using kieselguhr, I may substitute therefor, other powdered heat insulating materials, such as magnesia, alumina, asbestos or the like, and

I contemplate also the use of powdered material together with slabs, bricks or irregular-shaped pieces of insulating material,l` lwhich may be used to cover the surface of the carbide, the powdered material serving to fill the crevices between the slabs and the like to complete the seal, and any variation of such a procedure is within the invention herein set forth. The use thereof is not confined to the method of fixation of nitrogen above 'set forth, as it is equally well adapted for use in other reactions where it is desired to protect a heated surface against the' loss of heat and oxidation by air or contact with atmospheric moisture. These and other changes may be made in my invention without departing from the spirit thereof.

` What I claim is:

1. The method of making calcium cyanamide or the like which comprises placing ground calcium carbide in a container, covering the same with a layer of comminuted insulating material, and causing the carbide to react with nitrogen.

2. The method of making calcium cyan'- amide or the like which comprises placing ground calcium carbide in container, covering the same with a layer of comminuted kieselguhr, and causing the carbide to react with nitrogen.

3. The method of making calcium cyanamide or the like which comprises placing ground calcium carbide in a container, covering the same with a relatively thin layer of comminuted insulating material, and causing the carbide to react with nitrogen.

4:. The method of making calcium cyanamide or the like which comprises placing ground .calcium carbide in a container, covering the same with a relatively thin layer ot' kieselguhr and causing the carbide to react with nitrogen.

5. The method of making calcium cyanamide or the like which comprises placing ground calcium Y, carbide in a container,

lcovering the same with a layer of comminuted insulating material, and causing the carbide to react with nitrogen to form a block, removing the block and separating the comminuted material therefrom.

6. rThe method of.r making calcium cyanamide or the like which comprises placing ground calcium carbide in a container, completely covering the same with a layer of comminuted insulating material, and causing the carbide Ato react With nitrogen.

7. The method of making calcium cyan- -amideor the like which comprises placing lamide or the like which comprises 'placing in a container the material to be acted upon, covering the same with a layer of comminuted material'ada'pted to heat insulate the Surface of said iirst mentioned material and prevent access of air thereto, and heating the same to cause a reaction to take place.

In testimony whereof, I have hereunto subscribed my name this 15th day of June, 1925.

GEORGE E. cox. 

